1. Field of the Invention
The present invention relates to a method of manufacturing a compound semiconductor material, and more particularly, to a method of manufacturing a low resistivity p-type compound semiconductor material.
2. Description of the Prior Art
Most of the semiconductor devices such as light emitting diode, laser diode, photodetector, and transitior normally need some layers doped with n-type dopants and some layers doped with p-type dopants. However, some III-V and II-VI compound semiconductor materials are difficult to dope the p-type impurity in high carrier concentration, or even can""t achieve p-type conductivity. For example, p-type InP, AlGaInP and AlGaInN III-V compound semiconductor materials and ZeSSe II-VI compound semiconductor materials are some typical examples that are either difficult to achieve high p-type conductivity or even impossible to get the p-type conductivity. One of the major reasons why it is difficult to achieve high earner concentration in these p-type doping materials is attributed to the unintentional hydrogen incorporation and resulting acceptor passivation which occurs during the epitaxial growth or after the cool-down process of growth.
The influence of the cooling ambiance on the passivation of Zn acceptors in InP grown by atmospheric-pressure OMVPE was first studied by Antell et al. [Appl. Phys. Lett., 53, (1988), 758] and Cole et al. [Electron. Lett., 24, (1988), 929]. They found that the p-type InP layer capped with a p-type InGaAs and cooled down in an AsH3 ambiance, the hole carrier concentration could be significantly reduced by about 80% compared to a Zn-doped InP layer with a n-type cap layer. The hole carrier concentration can be recovered to the expected value simply by annealing in nitrogen atmosphere.
The hydrogen passivation is.even more serious in a p-type AlGaInP material, especially in a high aluminum content AlGaInP material. Hamada et al. [IEEE J. Quantum Electron. 27, (1991), 1483] found that the degree of passivation increased with aluminum composition. An increase in hole carrier concentration after annealing at 500 degree centigrade was observed and proved by a decrease in hydrogen content using SIMS analysis.
The hydrogen passivation effect is the most serious issue in AlGaInN materials. It causes the AlGaInN materials failed to achieve p-type conductivity. Amano et al. [Japanese J. Appl. Phys. 28, (1989), L2112] used low energy electron beam irradiation (LEEBI) to convert the compensated Mg-doped GaN into conductive p-type material. However, with acceleration voltage of 5 kV-15 kV, an electron beam can only reach a depth of about 0.5 xcexcm. In device design, normally a p-type GaN material with a thickness of more than 0.5 xcexcm is necessary. Therefore, LEEBI is not an effective way to convert the thick high resistivity Mg-doped GaN material into p-type conducting material. Besides, the conversion of the p-type GaN material is achieved by scanning the electron beam across the whole wafer. This electron beam scanning method is a quite slow process. It is very difficult to be adapted into the mass production process by the electron beam scanning method.
In U.S. Pat. No. 5,306,662, Nakamura et al. disclosed a method for reducing the resistivity of the p-type GaN by an annealing process in a nitrogen atmosphere over 400 degree centigrade approximately. But to be more effective, the annealing process should be carried out in the temperature range of 600-1200 degree centigrade.. Therefore, it is not suitable for III-V compound semiconductor materials that have high dissociation pressure at low temperature without a protective cap layer.
It is therefore a primary objection of the present invention to provide a method of manufacturing a low resistivity p-type compound semiconductor material to solve the above mentioned problem.
According to the first aspect of the present invention, there is provided a method of manufacturing a low resistivity p-type compound semiconductor material over a substrate. The method of the present invention comprises the steps of:
forming a p-type impurity doped III-V compound semiconductor layer on the substrate; and
applying a microwave treatment over the p-type impurity doped III-V compound semiconductor layer.
According to the second aspect of the present invention, there is provided a method of manufacturing a low resistivity p-type compound semiconductor material over a substrate. The method of the present invention comprises the steps of:
forming a p-type impurity doped II-VI compound semiconductor layer on the substrate; and
applying a microwave treatment over the p-type impurity doped II-VI compound semiconductor layer.
According to the third aspect of the present invention, there is provided a method of manufacturing a light emitting diode. The light emitting diode comprises a substrate, a n-type lower cladding formed on the substrate, and an active layer formed on the n-type lower cladding layer. The method of the present invention comprises the steps of:
forming an p-type impurity doped upper cladding layer on the active layer; and
applying a microwave treatment over the p-type impurity doped upper cladding layer.
According to the fourth aspect of the present invention, there is provided a method of manufacturing a light emitting diode. The light emitting diode comprises a substrate. The method of the present invention comprises the steps of:
forming an p-type impurity doped lower cladding layer on the substrate;
applying a microwave treatment over the p-type impurity doped lower cladding layer;
forming an active layer on the p-type impurity doped lower cladding layer; and
forming an n-type upper layer on the active layer.
The present invention provides a simple and effective way to convert the high resistivity p-type impurity doped III-V or II-VI compound semiconductor materials into conductive p-type materials. According to the present invention, the p-type impurity doped III-V or II-VI compound semiconductor materials are grown by either hydride vapor phase epitaxy (HVPE), organometallic vapor phase epitaxy (OMVPE), or molecular beam epitaxy (MBE). The p-type impurity doped III-V or II-VI compound semiconductor materials normally have high resistivity due to hydrogen passivation effect. The high resistivity p-type impurity doped III-V or II-VI compound semiconductor materials are then treated in a microwave apparatus for a period of time in order to convert them into high conductive p-type materials.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment which is illustrated in the various figures and drawings.